Ultrafast pulse phase shifts in a charged-quantum-dot–micropillar system

We employ a quantum master equations approach based on a vectorial Maxwell-pseudospin model to compute the quantum evolution of the spin populations and coherences in the fundamental singlet trion transition of a negatively charged quantum dot embedded in a micropillar cavity. Excitation of the system is achieved through an ultrashort, either circularly or linearly polarized resonant pulse. By implementing a realistic micropillar cavity geometry, we numerically demonstrate a giant optical phase shift ($\ensuremath{\sim}\ifmmode\pm\else\textpm\fi{}\ensuremath{\pi}/2$) of a resonant circularly polarized pulse in the weak-coupling regime. The phase shift that we predict considerably exceeds the experimentally observed Kerr rotation angle $(\ensuremath{\sim}{6}^{\ensuremath{\circ}})$ under a continuous-wave, linearly polarized excitation. By contrast, we show that a linearly polarized pulse is rotated to a much lesser extent of a few degrees. Depending on the initial boundary conditions, this is due to either retardation or advancement in the amplitude buildup in time of the orthogonal electric field component. Unlike previous published work, the dominant spin relaxation and decoherence processes are fully accounted for in the system dynamics. Our dynamical model can be used for optimization of the optical polarization rotation angle for realization of spin-photon entanglement and ultrafast polarization switching on a chip.